Jamieson, Fausset and Brown on 1 Chronicles 21:28

28. when David saw that the Lord had answered him ..., he sacrificed there--or, "he continued to sacrifice there." Perceiving his sacrifice was acceptable, he proceeded to make additional offerings there, and seek favor by prayer and expiatory rites; for the dread of the menacing angel destroying Jerusalem while he was absent in the center of worship at Gibeon, especially reverence for the Divine Being, led him to continue his adorations in that place which God (2Ch 3:1) had hallowed by the tokens of His presence and gracious acceptance.